there is no requirement neither in the quran nor the sunnah of the prophet to make a 'verbal' niyyah for prayer or fasting. However since actions are by intentions, all you need to have is the intention in your heart. and allah knows best.

sidenote: since actions are by intentions, therefore hanafi ulema do hold that verbal niyyah should be made, but it is still not obligatory, just a recommendation in case you think you'll forget to make the niyyah in your heart.